Vowel context, place difference, and the perceptual distinctiveness of sibilants

Vowel contexts are shown to influence the perceived distinction of sibilants at different places, e.g., with alveolar vs. palatal sibilants perceptually less distinct in the [_i] context than in the [_a] context. This study investigates if this pattern holds across different sibilant place contrasts, e.g., an alveolar-palatal contrast vs. an alveolar-retroflex contrast. Twenty-four listeners completed a speeded-AX discrimination task in which the stimuli were the sound pairs [si-ɕi] [sa-ɕa] [si-ʂi] [sa-ʂa], which aimed to access the relative psychoacoustic distinction of these pairs. The [si-ɕi] pair turned out to introduce a lower accuracy and a longer response time than the other pairs, with no response time difference among the other three. Assuming a longer response time to indicate less perceptual distinctiveness, the results confirm the observation in the literature that a [si-ɕi] pair is perceptually less distinct than a [sa-ɕa] pair; the lack of difference in [si-ʂi] vs. [sa-ʂa] suggests that the [_i] context does not reduce the perceived sibilant place distinction across all places. There seems to be a trading relation between the effect of vowel context (e.g., a reduced distinction in the [_i] context) and the relative acoustic difference between sibilants when evaluating the distinctiveness of a CV pair.